This invention relates to a method and apparatus for cooling hot lengths of rolled workpieces, such as rails and structural shapes, through maximum utilization of a cooling bed embodying a construction and having facilities to handle workpieces more efficiently on the cooling bed for either complete cooling of certain workpieces, such as structural shapes or partial cooling of other workpieces such as rails which undergo continued specialized cooling in facilities adjacent the cooling bed.
Because of the capital investment required for a rolling mill installation, it is desirable to utilize the facilities to produce different hot-rolled products having varying cross-sectional configurations. For example, one class of product, namely structural shapes including beams, and a second class of product, namely rails, can be processed at different times in the same rolling mill installation after suitable set-up operations including roll changing. The same cooling facilities for the workpieces can be used, at least in an initial cooling phase, to reduce the temperature of the workpieces down to a desired temperature. Rails intended for railroad service require controlled cooling within a temperature range of not less than 725.degree. F. down to at least 300.degree. F. This cooling process was developed to prevent the formation of shatter cracks, also called internal thermal ruptures, flakes, or internal thermal cracks. In mill operations, the rails are allowed to cool to about 1000.degree. F. and then the rails are placed in either stationary or movable insulated containers. Each rail must be placed in the container within a temperature range of between 1000.degree. F. and 725.degree. F. Thermocouples are placed between tiers of rails in the slow-cool container in order to obtain temperature readings during cooling. The containers are usually insulated to meet the specific cooling cycle. One such cycle requires that the temperature of the rails does not fall below 300.degree. F. in seven hours for rails at 100 pounds per yard in weight or heavier from the time the bottom tier is placed in the container. Five hours are required to cool rails to a temperature not below 300.degree. F. in the containers according to another cooling cycle when the rails are less than 100 pounds per yard in weight. The rails usually remain in the cooling containers for a minimum of 10 hours. Complete records are maintained of the cooling cycle for the rails in each container.
The problem occurs, however, as to the manner and facilities which are needed to cool the rails from the elevated temperature at which they arrive at a cooling bed down to the desired temperature at which the rails are placed in the cooling boxes. Thus, it is necessary to subject the rails to one cooling rate over a first temperature range and thereafter to a different cooling rate over a second temperature range. Since different apparatus is required to carry out the cooling of the rails at the second temperature range, it is necessary to keep the rails moving while cooling over the first temperature range to make room for further products coming from the mill and avoid a bottleneck in the mill-processing line. In a rolling mill installation for producing rails and beams, it has been proposed to use a cooling bed to cool rails from a cooling bed entry temperature of about 1800.degree. F. down to a temperature of about 90.degree. F. A delivery roller table incorporated into the cooling bed is used to discharge the rails transversely to their movement across the bed. After the rails are removed from the cooling bed, they are rotated to a head-up position and then packed into groups of about eight rails to form a layer which is then lifted by an overhead crane equipped with magnets and loaded into cooling boxes. Usually, two packing beds are required because while a group of rails from one packing bed is loaded into a cooling box, a layer of rails is accumulated on the other packing bed to assure loading of the rails into the cooling boxes at an optimum entry temperature. The present invention eliminates the need for packing beds as well as the conveying tables needed to remove rails from a cooling bed, thereby eliminating a substantial capital investment required for the specialized handling of rails while, at the same time, providing an improved method and cooling bed apparatus which are capable of carrying out the required treatment of rails and beams or other rolled structural shapes.
To minimize damage to the hot lengths of rolled shapes, it has been proposed to use a walking-beam type cooling bed incorporating a rectangular pickup and set-down pattern and by adjusting the speed of operation by the movable members of the walking-beam bed, the range of residence time for the hot-rolled shapes being controlled to meet cooling requirements. Since wide-flange beams, for example, are cooled to ambient temperature on the cooling bed, the length of the cooling bed with respect to the direction of movement of the hot lengths of beams is selected for the necessary residence time to cool the beams. As the temperature of the beams is reduced during movement across the cooling bed, there is also a concurrent reduction to the possible damage to the beams because of contact with members used to advance the beams. Thus, it is practical to construct the cooling bed with a first section incorporating a design of a walking-beam type bed and a downstream section of a different design with a chain conveyor or similar mechanism for advancing the beams in succession along the bed. However, two distinct drive systems are used each in a different area to advance workpieces across the entire bed. A mechanical failure to one drive system adversely affects complete unloading of rolled workpieces from the bed.